1. Field of the Invention
The present invention relates to a fixing member, a fixing apparatus, and an image forming apparatus having an outermost layer made of fluorine type resin on a fixing belt.
2. Discussion of the Background Art
A fixing apparatus is a well known device that pressure contacts a fixing member, such as a fixing belt, a fixing roller, etc., and fixes a toner image onto a transfer member. For example, a fixing apparatus discussed in Japanese Patent Application Laid Open No. 2002-268436 includes an endless fixing belt wound around a fixing roller having smaller belt curvature and a heat roller that applies heat and pressure contacts to heat and fix a toner image onto a transfer member. Such a fixing belt is generally formed from a base member made of heat resistant resin such as polyimide or metal, a heat resistant elastic layer such as rubber, elastomer, etc., and a releasing layer (i.e., an outermost layer) made of fluororesin. The releasing layer made of the fluororesin is formed by steps of producing a fluororesin tube by extrusion, wrapping the above-mentioned elastic layer with the fluororesin tube, and applying heat and melting (i.e., burning) the fluororesin. Otherwise, the releasing layer is formed by coating fluororesin particles with a spray to an elastic layer, and then burning the fluororesin. By forming the releasing layer with the fluororesin in such ways, a fixing belt having excellent releasing and heat resistant performances can be obtained. However, since the fluororesin lacks flexibility, crack appears on the releasing layer and belt flexibility becomes insufficient when it is wound around the fixing and heat rollers having small belt curvature for a long time. To resolve such a problem, various countermeasures have been attempted. For example, Japanese Patent Application Laid Open No. 2003-167462 discusses a fixing belt that employs a releasing layer made of fluororesin having a melt flow rate (MFR) of less than three to avoid crack even when the release layer is used for a long time.
However, since fluororesin of a low temperature melting type with a small MFR lacks fluidity when melting, the fluororesin melted during burning does not flow, and accordingly spoils smoothness of the fixing belt. As a result, unevenness occurs in brilliance on a fixed image on a transfer sheet when the fixing belt with poor smoothness fixes these images. Such problem is also found in a fixing roller.